(572d) Toughening of Polyamide-6 With Poly(styrene-alt-maleic anhydride)-Polystyrene-Block-Poly(n-butyl acrylate)-Block-Polystyrene Copolymer (SMA-SBAS) Synthesized Via RAFT Mini-Emulsion Polymerization

Poly(styrene-b-butadiene-b-styrene)
(SBS) triblock copolymers is one of the main commercial thermoplastic
elastomers (TPE) due to their excellent mechanical properties, and commonly used
as impact modifier for polyamides with maleic anhydride grafting through reactive
blending. The impact performances of polyamides can be greatly
enhanced by filling with block copolymers.

On the other hand,
controlled/living radical polymerizations (CLRP) have been investigated
extensively over the last few years because these methods are compatible with
almost all types of vinyl monomers and with emulsion polymerization processes
where water is used as polymerization media.

Well-designed amphiphilic
block copolymers, in analogy to water/oil emulsions, create novel
nanostructured blends in a few minutes of mixing. Block copolymers, embedded
into polyamide matrix, produce the cocontinuous nanostructure, and could have
great toughening effects without altering significantly the elastic modulus.

Based on the method of
reversible addition-fragmentation chain transfer radical polymerization (RAFT),
the styrene/butyl acrylate block copolymer (SMA-SBAS) was successfully
synthesized, mediated by maleic anhydride/styrene alternating copolymer (SMA)
as the amphiphilic co-oligomer macroRAFT agent. After melt mixing,
PA-6/SMA-SBAS blends achieve an ideal dispersion of the scale in the polyamide
matrix and significantly improve the impact strength, with decreased water
absorbency. The influence of the rubber content (butyl acrylate), block copolymer
chain length is investigated. SEM results showed the major toughening
mechanisms, TEM observations indicates that SMA-SBAS particles self-assembled
the cocontinuous nanostructure in the polyamide matrix due to phase separation.
This work demonstrated that the RAFT mini emulsion polymerization holds good
promise for synthesis of unique structures of block copolymers, which makes
affordable engineering polymer blends with extraordinary performance. Compared
to current industrial process, SBS synthesis by anionic polymerization, compatilizer
introduced by melt grafting, the TPE impact modifier synthesized by RAFT
emulsion process would like to be energy-saving and environmentally friendly.

Graph 1: Synthesis of the
macroRAFT agent

Graph 2: Synthesis of SMA-SBAS
amphiphilic copolymer